1. Field of the Invention
The present invention relates to generation of a virtual viewpoint image from an image captured by an imaging unit having distortion characteristics and ambient light amount decrease characteristics (vignetting), based on distortion characteristics and ambient light amount decrease characteristics of a virtual camera.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2004-088247 discusses a system to capture an identical scene by using a plurality of cameras and to display a video viewed from a moving virtual viewpoint (free viewpoint image). The simplest method to realize such system is arranging a plurality of cameras and continuously reproducing videos captured by these cameras while switching these cameras. As discussed by Japanese Patent Application Laid-Open No. 2004-088247, such an image reproducing apparatus adjusts brightness or color between different cameras to execute smooth video reproduction.
In addition, Japanese Patent Application Laid-Open No. 2008-217243 discusses image processing with use of a virtual camera arranged between cameras. According to this document, in addition to videos captured by real cameras, a video viewed from a virtual viewpoint is generated and used to increase continuity. In addition, according to a widely known technique of generating a virtual viewpoint video, object distance information is acquired from videos captured by a plurality of cameras and rendering is executed. When generating a virtual viewpoint video, since correspondence between a point on a virtual viewpoint video and a point on a real camera video is calculated geometrically, distortion and the like present in the real camera video are corrected. Since the virtual viewpoint video is subjected to geometrical projective transformation, a video without distortion as if captured by a pinhole camera can be created.
However, in such video without distortion created by projective transformation as if captured by a pinhole camera, object deformity of peripheral parts of the video is larger than that of a video captured by a real camera. As a result, the video appears unnatural. In addition, if object distance information is not successfully acquired, the virtual viewpoint video cannot be generated. Thus, it is difficult to create stable videos.